Most often people use UITable views with custom cells for such UI interaction. Four fields on one row on an iPhone in portrait mode may be tight, so people play with multiline layouts for the cell. I suppose you could also allow for horizontal scrolling but that doesn't sound like a UI I'd like to deal with as a user.

For the data storage, you could use CoreData. It even has a feature to handle that fourth calculated value. If your needs are small, you could simply archive your model objects, use flat files, or use plists. If you have SQL experience, you could use SQLite directly.

BTW, the 'add' button usually goes on the top left on the navigation bar. See Apple's Contacts or Notes apps. Pay attention to what changes on the nav bar after you tap that button. Their Mail app effectively has that button on the lower tab bar.

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